Topband: T Top Verticals and yagis

[Paul Christensen]

I would hate to give up the efficiency of an over-resonated T, even if field strength isn’t significantly better than an L design.   I think two design issues help to avoid pattern distortion to nearby HF Yagis.  

First, as Frank suggested, keep the length of the horizontal T wire non-resonant on any given band, including non-harmonically related bands like 30m.  It's not necessary to select a T top wire length that results in resonance at the base feed, at least with a single omni antenna.   

Secondly, there's a difference in interaction between a T that's installed broadside to a Yagi versus one that's installed perpendicular off the end of a Yagi.  For example, If a T is installed between two towers that are spaced 150 ft apart and a 40m Yagi is atop one of the towers, the T top wire is never broadside to the Yagi.  It's looking straight down a piece of wire.  

It's no different than a Yagi director that's rotated 90 degrees to the driven and reflector elements.   In fact, an existing Yagi design file could be modeled that way only with a rotational change to the director's Cartesian coordinates and a  change in distance from the DE.  No doubt modeling will still show some interaction but what remains should be cured with an optimum, non-resonant director length.  

Paul, W9AC           

-----Original Message-----
From: Topband <topband-bounces+w9ac=arrl.net at contesting.com> On Behalf Of Guy Olinger K2AV
Sent: Friday, February 28, 2020 12:16 PM
To: W7RH <midnight18 at cox.net>
Cc: topband at contesting.com
Subject: Re: Topband: T Top Verticals and yagis

That’s an awful lot of effort just to keep a T top. There are a number of effective alternatives to the traditional T top without the interaction drawbacks. Inverted L is only the dirt simple one without the skip-zone-making high angle hole in the pattern.

73, Guy K2AV

On Fri, Feb 28, 2020 at 9:46 AM W7RH <midnight18 at cox.net> wrote:

> The discussion has involved horizontally polarized Yagis. Perhaps use 
> a vertical 8 circle array on 40m! LOL And keep your T-Top!
>
> Bob, W7RH
>
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